1. Field of the Invention
This invention relates generally to co-laminated films. More particularly, the present invention relates generally to co-laminated film for bags. More particularly, the present invention relates generally to co-laminated film for trash bags.
2. Description of the Related Art
Laminates have been described in the prior art in order to achieve improved overall stiffness and tear resistance. Although lamination of uniaxial layers improves tear resistance transverse to the direction of stretching, tearing is easily effectuated along the longitudinal axis of stretching. Biaxial orientation of laminates improves stiffness and tear resistance in two directions, but the laminate is still highly susceptible to tears which run longitudinally along the combination of the axes. Further, the biaxial orientation methods used are not easily adaptable to high speed production processes.
The prior art extensively describes the importance of continuous and complete lamination. U.S. Pat. No. 5,100,721 to Akao describes a laminated film comprising a pair of coextruded multilayer inflation film layers disposed symmetrically and joined by blocking which provides a film that is excellent in physical strength and bag rupture strength. Akao describes the problems when the film layers are not completely laminated, describing that unless the area joining the inner layers of the inflation film to each other by blocking is rendered more than 95%, wrinkling and the separation at the blocking portion frequently occur in the lamination process caused by the air remaining in the unjoined portion.
Discontinuous lamination is described in U.S. Pat. No. 7,306,729 to Bacino et al. by applying a discontinuous lamination adhesive across the surface of the layers to bond layers to a membrane. U.S. Pat. App. 2007/0166503 to Hannigan describes laminating a lining material to a barrier layer through a coating method or by use of an adhesive, where the lamination may be performed using continuous or discontinuous lamination methods. U.S. Pat. App. 2008/0124461 to Leener describes the discontinuous lamination of credit cards. PCT publication WO1999056953 to Hoffman describes laminating corrugated sheets of paper to printed paper in a discontinuous lamination process using an applied adhesive layer. U.S. Pat. No. 4,302,495 to Marra describes discontinuous or spot bonded lamination can be provided by using an engraved pressure roll with a smooth backup roll to form a two layer nonwoven fabric from a melt-blown polypropylene microfiber mat and a directionally oriented thermoplastic netting layer. PCT publication WO199013702 to Rasmussen describes a process for the discontinuous lamination of technical textiles with adhesives.
Thermoplastic film, microporous film, and laminates thereof, are described in U.S. Pat. 2002/0074691 to Mortellite et al. Relevant patents regarding extrusion lamination of unstretched nonwoven webs include U.S. Pat. Nos. 2,714,571; 3,058,868; 4,522,203; 4,614,679; 4,692,368; 4,753,840 and 5,035,941. The above '868 and '368 patents disclose stretching extruded polymeric films prior to laminating with unstretched nonwoven fibrous webs at pressure roller nips. The '203 and '941 patents are directed to co-extruding multiple polymeric films with unstretched nonwoven webs at pressure roller nips. The '840 patent discloses preforming nonwoven polymeric fiber materials prior to extrusion laminating with films to improve bonding between the nonwoven fibers and films. More specifically, the '840 patent discloses conventional embossing techniques to form densified and undensified areas in nonwoven base layers prior to extrusion lamination to improve bonding between nonwoven fibrous webs and films by means of the densified fiber areas. The '941 patent also teaches that unstretched nonwoven webs that are extrusion laminated to single ply polymeric films are susceptible to pinholes caused by fibers extending generally vertically from the plane of the fiber substrate and, accordingly, this patent discloses using multiple co-extruded film plies to prevent pinhole problems. Furthermore, methods for bonding loose nonwoven fibers to polymeric film are disclosed in U.S. Pat. Nos. 3,622,422; 4,379,197 and 4,725,473. It has also been known to stretch nonwoven fibrous webs using intermeshing rollers to reduce basis weight and examples of patents in this area are U.S. Pat. Nos. 4,153,664 and 4,517,714. The '664 patent discloses a method of incremental cross direction (CD) or machine direction (MD) stretching nonwoven fibrous webs using a pair of interdigitating rollers to strengthen and soften nonwoven webs. The '664 patent also discloses an alternative embodiment wherein the nonwoven fibrous web is laminated to the thermoplastic film prior to intermesh stretching.
One large use of plastic films is as thermoplastic bags for liners in trash or refuse receptacles. Trash receptacles that employ such liners may be found at many locations, such as, from small household waste baskets and kitchen garbage cans. The trash canisters are typically made from a rigid material such as metal or plastic. Bags that are intended to be used as liners for such refuse containers are typically made from low-cost, pliable thermoplastic material. When the receptacle is full, the thermoplastic liner actually holding the trash can be removed for further disposal and replaced with a new liner. To avoid inadvertently spilling the contents during disposal, the bags must be tear and puncture resistant. Trash bags are typically formed by employing two pliable plastic sheets joined on three sides (or a U-folded plastic sheet joined on two sides) and open on the remaining side.
Another use of plastic films is as flexible plastic bags for storing food items, either temporarily as in the case of packaging snacks or long term as in the case of freezer storage. Plastic bags of this style typically include flexible sidewalls made from, for example polyethylene, that define an opening and an internal volume accessible through the opening, an example of which is described in U.S. Pat. No. 6,385,818 to Savicki Sr. To seal the bag, interlocking closure strips may be provided about the rim of the opening.
As is clear from the above discussion, continued technology improvement is needed to address the unique problems associated with improving the tear and puncture resistant of films, especially for trash bags.